How does squared samples "make tweaking easier?"
All it does is square the specified number of samples. So 10 samples becomes 100 samples.

From the commit log:


  Cycles / Sampling UI:  
  
  Add a "Squared Samples" option to the UI, to use squared values for ease of use. This can make it easier from an artist point of view, to weak settings. 
  
  With this enabled, all Sample values will be squared. So 10 Samples become 100 Samples.
  For the Non-Progressive Branched Path integrator: 4 AA Samples * 5 Diffuse Samples would become 16 AA Samples * 25 Diffuse = 400 in total.


Also see this related post and this thread on the bf-cycles mailing list